We've had a sheet of glass in our triple glazed windows shatter, no sign of physical damage, it's a 3+1 system; a sealed triple glazed unit then blinds, then another pane on the outside. The pane that shattered is the outermost of the triple glazed unit.

The window manufacturers have said they're not responsible, and anyway warranty is only 3 years. Cost is almost 2k, money I need to do other stuff with right now.

I'm thinking of claiming on household insurance, but do I then need to imply that the breakage occurred as a result of an accident?

If it's shattered on its own it could well be how it was installed. Glazed units need to be supported well and the frames need to not move too much. I would have though it would have been covered by standard insurance, like tiles blowing off, rather than an accident.

shopping around for a new unit or someone who can fix that one seems the next option ,you do have 2 sheets of glass left it might be possible to "demount"those and then it is only 1 sheet and a new "mount"to buy .

im a bit unsure of my memory but i think a chum mentioned mending sealed units with the undamaged parts when he was in the window building game.

it might be worth asking(otherwise it will be a new one and the lid of a rather posh cold frame for the garden)